Sensor device for spacial imaging of endoscopes

ABSTRACT

A sensor device and system projects a three-dimensional image of the position of the colonoscope within the gut onto a video screen next to the optical image from the end of the colonoscope. The sensor device comprises a plurality of strain gages mounted on a bendable rod at the head of the rod. As the head is pushed through the biopsy channel of the colonoscope, the head bends with the curvature of the colonoscope causing the deformation of the head to be captured by the strain gages. An encoder at the inlet to the biopsy channel records the velocity and distance of the head as the head is pushed in and through the channel. The combined electrical output from the strain gages and encoder enables an instantaneous generation of a three-dimensional image of the colonoscope on a view screen. The sensor device avoids the need for any equipment that is above or surrounds the abdomen of the patient.

BACKGROUND OF THE INVENTION

The field of the invention pertains to endoscopes and, in particular, tothe position of an endoscope as it is advanced through an orifice in thehuman body. The position is of particular importance in advancing acolonoscope through the gut because of the convoluted shape of the gutand the danger of damage to the gut wall at locations of steep curvatureand loop.

A variety of techniques have been used to visualize the colonoscope asit is advanced in the gut. Perhaps the most obvious technique isfluoroscopy. Unfortunately, fluoroscopy requires expensive, bulky andawkward equipment externally positioned over the patient. Fluoroscopetime is generally a scarce resource in even the best equipped medicalcenters. Most important is the extended time period of x-radiationexposure to the patient, endoscopist and other hospital personnel.

To avoid the use of fluoroscopy other approaches to measuring theposition and, in particular, the curvature of the colonoscope as it isadvanced through the colon have been proposed. Magnetic field sensorshave had some experimental development. In one approach, miniatureinductive sensors were placed within the biopsy channel of an endoscope.A magnetic field was created around the exterior of the patient. As thesensors were moved through the biopsy channel an electric signal wasgenerated and the signals monitored by a computer which calculated thepath of the sensors as they moved through the biopsy channel. Since thebiopsy channel follows through the endoscope, the position andconfiguration of the endoscope can be generated by the computer toprovide a three dimensional image of the endoscope. This magnetic fieldsensor is disclosed in Bladen, I. S. et al.: "Non-Radiological TechniqueFor Three Dimensional Imaging Of Endoscope", The Lancet, pp. 719-722,Vol. 341: Mar. 20, 1993.

A similar study was done with a magnetic field and coil to generate animage of the endoscope in the colon during motion of a sensor rod. Thisstudy was reported in Williams, Christopher, et al.: "ElectronicThree-Dimensional Imaging Of Intestinal Endoscope", The Lancet, pp.724-725, Vol. 341: Mar. 20, 1993.

The magnetic approach has several disadvantages. The first system aboverequires several low frequency magnetic field generators in order toobtain the signals from the sensor. Thus, the system is expensive andcumbersome with portions that cover the patient's entire abdomen thusinterfering with the endoscopic procedure. Moreover, a nonmetallicoperating platform or bed is required and the patient must not moveduring the detection period. Similar problems arise with the secondsystem above.

Devices to measure the curvature of pipes without external fielddevices, whether radiative or magnetic, have been developed forinspecting steam generators in nuclear power facilities. Disclosed inU.S. Pat. No. 4,651,436 is a bendable plug that is moved through a pipe.As the plug moves and bends, sensors communicate the changes in bendingof the plug to electrical measurement means for the sensors. Inparticular, FIG. 5 shows strain gages on the exterior of a flexibletube.

U.S. Pat. No. 4,910,877 shows a similar flexible device adapted to passthrough steam generator pipes and provide an electrical signal from astrain gage as the device negotiates bends in the pipes. These devices,however, are relatively large, on the order of inches in diameter, andneed only negotiate a few degrees of bend.

More directly related to endoscopes and measurement of the position andposture of the device is U.S. Pat. No. 5,060,632 wherein FIG. 101 showscurvature sensors on the exterior of a bendable portion near the tip ofthe endoscope. The bent state is monitored electrically as the externalcontrols on the endoscope are manipulated to bend the endoscope duringadvancement. Thus, the curving path of the head of the endoscope can bemonitored as the head advances. Means to cause the head to bend are alsoshown in U.S. Pat. No. 4,873,965.

SUMMARY OF THE INVENTION

The principal object of the new sensor device is a simple, easy to usevisualization system which projects a three dimensional image of theposition of the colonoscope onto a video screen next to the opticalimage from the end of the colonoscope.

Further objects of the new sensors comprise a device that avoids use ofan "external field" or any equipment that surrounds or is positionedabout the patient. Only the colonoscope itself is positioned inside andadjacent the patient.

Moreover, the new sensor device may be employed with existingcolonoscopes because the sensors are moved through the biopsy channel ofthe colonoscope. An important feature of the sensors is the option ofadvancing and retracting the sensors within the colonoscope as thecolonoscope is periodically advanced or withdrawing and reinserting thesensors as necessary when the biopsy channel is to be used for otherpurposes.

The sensor device comprises a plurality of sensors in the form of tinystrain gages mounted on a bendable rod at the head of the rod. As thehead is pushed through the biopsy channel of the colonoscope the headbends with the curvature of the colonoscope causing the deformation ofthe head to be captured by the strain gages. The instantaneousdeformation of the strain gages can be captured electrically as the headis pushed through.

An encoder at the inlet to the biopsy channel records the velocity anddistance of the head as the head is pushed in and through the channel.The combined electrical information from the strain gages and encoderenables an instantaneous generation of a three-dimensional image of thecolonoscope. This image can be placed on a view screen convenient to thephysician operating the colonoscope.

The cross-sectional area of the sensor rod can be reduced in size toallow insertion into the smallest biopsy channels including pediatricendoscopes. Thus, this sensor device can be used for all types ofendoscopy including small bowel enteroscopy wherein the tortuosity ofthe small bowel causes particular difficulty.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the overall structure of the imaging system for thesensor device;

FIG. 2 illustrates the basic structure of the sensor rod;

FIG. 3 illustrates the strain gage configuration on the head of thesensor rod;

FIG. 4 illustrates the sensor head and rod navigating the biopsy channelin a colonoscope;

FIG. 5 is a flow diagram of the basic software for the imaging system;

FIG. 6 is a flow diagram for the software that provides for threedimensional information on the view screen of the imaging system; and

FIG. 7 illustrates a mold half for the manufacture of the sensor rod.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts the sensor device or rod 10 and colonoscope inside apatient during use. The electric signals from the strain gages of thesensor device 10 are communicated to a strain gage signal processingcircuit 12 and then fed to a computer 16 for calculation and display ofan image 18 on a view screen 20.

A second set of electric signals from the optical encoder representingthe velocity and distance of the head of the sensor device as it isadvanced in the biopsy channel of the colonoscope is communicated to anencoder signal processing circuit 22. The encoder electric signals arethen fed to the computer 16 for the calculation and display of the image18.

Within the strain gage signal processing circuit 12 are a plurality ofWheatstone bridge circuits, each circuit having as one element anindividual strain gage of the sensor device 10. Where a large number ofindividual strain gages are employed the strain gage signal processingcircuit 12 may employ an analog multiplexer circuit controlled by thecomputer 16 to selectively and sequentially query the strain gages.

FIG. 2 depicts schematically the sensor device or rod 10 from head 24 toelectrical connector 26. The sensor rod 10 is constructed of siliconerubber having a stainless steel wire 28 down the center axis of the rod.The wire 28 reinforces the rod and substantially prevents the elongationof the rod 10. The wire 28 and silicone rubber is sufficiently flexibleto conform the rod 10 to the shape of the biopsy channel but return therod to a straight shape when retracted from the biopsy channel.

A plurality of strain gages 30, 32 are affixed to the exterior of therod 10 with wires leading to the electrical connector 26. The electricalconnector 26 interfaces with the signal processing board of the signalprocessing circuit 12. The strain gages 30 at the head 24 of the rod 10are positioned to measure bending as best shown in FIG. 3 wherein thegages are positioned at 90° intervals about the rod in one or more axiallocations. The portion of the rod 10 having the bending strain gages 30comprises the head 24. The base of the head 24 is a location spaced justbeyond the band of bending strain gages 30 most remote from the tip ofthe head. Torsional strain gages 32 are spaced along the length of therod 10.

The entire rod 10 is encased in a polytetrafluoroethylene coating 34 toprotect the strain gages 30, 32 from abrasion and liquids present in theenvironment. The coating also permits the rod 10 to be easily advancedand retracted through the biopsy channel. The coating may be coated ontothe rod in any conventional manner, however, a shrink fitpolytetrafluoroethylene tube has been found most advantageous andeconomical.

Adjacent the inlet 25 of the biopsy channel is the encoder wheels 27 and29 on opposite sides of the sensor rod 10. The encoder wheels 27 and 29are urged into firm contact with the sensor rod 10 by springs 23fastened to a base 19. One of the wheels 27 serves as an idler and theother wheel 29 drives an optical rotary encoder to provide an electricsignal in response to rotation of wheel 29. The rotation of wheel 29 iscaused by linear movement of the sensor rod 10 into the biopsy channel36. Thus, the encoder wheel 29 provides a measure of distance versustime for the movement of the head 24 through the biopsy channel 36.

As best shown in FIG. 3, the head 24 is about 100 mm in length asequipped with the bending strain gages 30. When the head is bent, asshown at 24', the gages to the inside of the curve are put incompression and the gages to the outside of the curve are put intension.

The torsional strain gages 32, however, are located beginning on thehead 24 and along the remaining portion of the rod 10 which may extend1500-1800 mm to the electrical connector 26. As noted above, the entirerod 10 assembly is encased in the polytetrafluoroethylene coating orshrink fit tube.

As shown in FIG. 4 the rod with the head 24 is advanced 10', 24' throughthe biopsy channel 36 of a colonoscope 38. In this mode of use, thecolonoscope 38 is not advanced as the sensor rod 10 is advanced. Oncethe head 24 of the sensor rod 10 reaches the tip of the colonoscope acomplete picture of the current location of the colonoscope will beobtained.

FIG. 5 depicts the overall software flow diagram for the computer 16.The main program to calculate the path of the rod 10 and head 24comprises the center vertical column of flow chart symbols beginningwith "Start" 41 and ending with "Finished insertion?" 43. The computer16 repeatedly reads the encoder wheel 29 position and strain gages 30and 32 to calculate the position of the circular tip of the head 24. Thecalculated tip position of the head 24 is displayed as an ellipse toindicate the posture of the circular tip of the head 24. The displayedcenter of the ellipse indicates the position of the tip and theorientation of the ellipse indicates the orientation of the plane of thecircular tip. The series of calculated and displayed centers of theellipses are the via points which depict the path of the head 24 as aline of points determined by distance from the inlet 25 of the biopsychannel 36. These points form the path of the display 18 on the viewscreen 20.

The side loops of the flow diagram provide useful additional features.The loop to the right 40 provides for a simulation program as a trainingaid by simulating the encoder output and the strain gage 30, 32 outputs.Such a built in software simulator provides an excellent training toolwithout the need for any additional hardware.

The upper loop to the left 42 is a calibration sequence for the sensorrod 10 and head 24. Since the rubber sensor rod 10 and head 24 aretypically more flexible than the strain gage 30, 32 elements fastened tothe rod 10 and head 24, the strain gages tend to slightly distort therubber in resisting the bending. As a result, these strain gages tend toreflect less bending than is actually occurring.

To calibrate, the sensor rod 10 and head 24 are deformed to a specifiedcurved shape and the actual output of the strain gages 30, 32 comparedwith calculated strain data for the curved shape. Each sensor rod 10 andhead 24 can be calibrated just before use thus assuring a more accuratedepiction of the sensor device 10 on the view screen 20.

The lower loop to the left 44 draws the tip circles as a series ofpoints about the tip point with each tip point iteration, the circlesactually appearing as the ellipses on the view screen. When the finaltip point is reached at the end of the biopsy channel, an optionalprogram at 46 connects the ellipses and shades the space therebetween toprovide a more realistic look to the image 18 of the colonoscope on theview screen 20.

Since a view screen 20 is two dimensional and the desire is to presentthree dimensional information to the viewer, the overall size of eachellipse depicts the distance from the viewer, more particularly, thedepth of the sensor rod 10 and head 24 below the wall of the abdomen ofthe patient. Thus, smaller ellipses represent greater depth within theabdomen. The user can thereby visually instantly judge depth within theabdomen.

FIG. 6 depicts the flow diagram for the optional creation of a morerealistic three dimensional image of the colonoscope. When the sensorrod 10 reaches the end of the biopsy channel 36, the entire path throughthe via points is calculated. Then the path between each two ellipses isdivided into twenty equal segments and an ellipse calculated for eachsegment. Using a Z-buffer algorithm to delete portions of ellipsesbehind other points and a three dimensional illumination and reflectiontechnique to shade the image, a realistic appearing three-dimensionimage of the colonoscope is displayed.

The calculation of the via and tip points is based on a kinematic modelusing the world coordinate system located at inlet 25 of the biopsychannel and the moving coordinate system on the head 24 at the base ofthe head. The position of the tip of the head 24 can then be calculatedfrom the outputs of the bending strain gages 30 on the head relative tothe moving coordinate system at the base of the head. The position andposture of the moving coordinate system is calculated and recorded. Atany time, the moving coordinate system is in the position that wasoccupied by the head in the previous time interval. The distance of thebase coordinate to its position in the previous time interval is theinsertion length which is measured by the encoder. Therefore, based onthe head position information from the previous time interval which iscalculated based on the bending strain gages, the relationship betweenthe moving coordinate system and the moving coordinate system in theprevious time interval can be calculated. In turn, through therelationship of the world coordinate system and the moving coordinatesystem the position of the tip on the sensor head 24 can be ascertainedwithin the patient's body. The calculation of the tip position isreiterated for intervals of time as the sensor rod 10 is pushed throughthe biopsy channel 36 until the end of the channel is reached. Sincedistance of the sensor rod 10 in the biopsy channel 36 is related totime by the encoder, the spacing or distance between the tip centerpoints of the ellipses can be controlled by the computer regardless ofthe speed with which the user pushes the sensor rod 10 into the channel.The computer calculates insertion distance from the encoder and repeatsthe tip center point and ellipse calculation for equal sequentialinsertion distances as the sensor rod 10 is pushed in the biopsy channel36.

To take account of the twisting of the sensor rod 10 between the worldcoordinate system and the moving coordinate system, the twist angles ofthe sensor rod 10 can be measured from the outputs of the torsion straingages 32 spaced along the length of the rod. These outputs can beinserted in the transformational matrix between the coordinate systemsto calculate the rotational twist of the moving coordinate systemrelative to the world coordinate system.

The preferred method of constructing the rod comprises a splitcylindrical cavity 50 the length of the sensor rod 10 as shown in FIG. 7wherein one of the mold halves is shown. The stainless steel wire 28 isbrought taught along the axis of the cavity 50. The strain gages 30 and32 are positioned in the mold halves and a suitable primer applied tothe strain gages and wire 28. The primer may be applied to the straingages 30 and 32 and the wire 28 before placement in the mold 50. Theprimer is selected for compatibility with the particular rubberformulation poured into the cavity 50 after the halves are broughttogether. Silicone rubber and urethane rubber have both been foundsuitable for the sensor rod 10. The primer is necessary to provide theadhesion necessary for the strain gages 30 and 32.

After the cured sensor rod 10 is removed from the cavity 50, thepolytetrafluoroethylene sleeve 34 is shrunk fit over the sensor rod 10,thus encasing the entire assembly in a protective and relativelyslippery surface for ease of insertion in the biopsy channel 36.

Although the sensor rod 10 has been described above as having torsionalstrain gages 32 spaced along substantially the full length of the rodwith bending strain gages 30 over a relatively short bending head 24other constructions can be envisioned. For example, referring back toFIG. 2 the head 24 may be formed as a separate part with the bendingstrain gages 30 there attached. The head 24 can then be attachedadhesively or mechanically to a relatively less expensive flexible rodlacking the torsional strain gages 32 and wire 28. This construction canbe used for imaging calculations that entirely do not require torsionaldata from the portion of the rod 10 behind the head 24.

By forming the head 24 as a separate part, a much shorter mold cavity 50and wire 28 can be used, thus saving considerable tool and materialexpense for the sensor rod 10.

I claim:
 1. In combination with an endoscope having a biopsy channeltherethrough,a sensor comprising a flexible rod, a plurality of straingages securely attached to the rod, at least some of the strain gagesmounted parallel to the axis of the rod to provide a change inelectrical impedance in response to bending of the rod, inelastic meansin the rod to substantially prevent elongation of the rod during bendingand means to measure the insertion distance of the sensor in the biopsychannel.
 2. The endoscope and sensor of claim 1 wherein the rod iscovered with a material easily slideable in the biopsy channel.
 3. Theendoscope and sensor of claim 1 wherein the strain gages are mounted onthe surface of the rod at a plurality of axial locations, wherein thestrain gages mounted parallel to the axis are located near one end ofthe rod and the other strain gages are generally spaced along the lengthof the flexible rod.
 4. The endoscope and sensor of claim 3 wherein thesurface of the rod and strain gages are covered with a material easilyslideable in the biopsy channel.
 5. The endoscope and sensor of claim 4wherein the material covering the rod and strain gages is shrunk fitthereover.
 6. The endoscope and sensor of claim 4 wherein the materialcovering the rod and strain gages is polytetrafluoroethylene.
 7. Theendoscope and sensor of claim 1 further comprising a second flexible rodlacking strain gages and affixed to one end of said flexible rod.
 8. Asensor for an endoscope having a biopsy channel, the sensor comprising abendable rod, a plurality of strain gages securely attached to the rod,at least some of the strain gages mounted to measure strain parallel tothe axis of the rod to provide a change in electrical impedance inresponse to bending of the rod,separate inelastic means extendinglongitudinally through the rod to substantially prevent elongation ofthe rod during bending, and means to measure insertion distance of thesensor in a biopsy channel, wherein at least some of the strain gagesare mounted to measure torsional strain of the rod to thereby provide achange in electrical output in response to twisting of the rod.
 9. Thesensor of claim 8 wherein the strain gages are mounted on the surface ofthe rod at a plurality of axial locations wherein the strain gagesmounted to measure strain parallel to the rod axis are located near oneend of the rod and the strain gages mounted to measure torsional strainof the rod are generally spaced along the length of the rod.
 10. Thesensor of claim 9 wherein the rod and strain gages are covered with amaterial easily slideable in an endoscope biopsy channel.
 11. The sensorof claim 8 wherein the strain gages mounted to measure strain parallelto the axis of the rod are located near one end of the rod.
 12. Thesensor of claim 11 wherein the rod and strain gages are covered with amaterial easily slideable in an endoscope biopsy channel.
 13. The sensorof claim 8 further comprising a second bendable rod lacking strain gagesand affixed to one end of said bendable rod.